The common ancestor of humans, monkeys, apes and other primates may have arisen much earlier than previously thought.

New research suggests the animals from which humans could have emerged were living in the tree tops 85 million years ago, when the dinosaurs still ruled the Earth.

What the earliest common ancestor might have looked like

Until now, the widely accepted date was 65 million years ago, about the time when the dinosaurs died out.

But a team of scientists in Britain and the United States has analysed gaps in the fossil record and come up with a new figure, some 20 million years earlier. It means the whole story of primate evolution may have to be rewritten.

The new theory challenges the idea that primates were unable to make their mark on the planet until after the demise of the dinosaurs.

It also suggests that continental drift played a role in how primates evolved in different parts of the world. It even has implications for our own descent - the first humans may have appeared about eight rather than five million years ago.

Jigsaw puzzle

The research, which was revealed in the scientific journal Nature, is based on a statistical analysis of evidence from the fossil record.

According to a computer model, no more than 7% of all primate species that ever existed have been dug up.

Co-author Robert Martin, of the Field Museum in Chicago, US, said current interpretations of primate and human evolution were flawed because palaeontologists had relied too heavily on direct interpretation of the known fossil record.

He said: "Our calculations indicate that we have fossil evidence for only about 5% of all extinct primates so it's as if palaeontologists have been trying to reconstruct a 1,000-piece jigsaw puzzle using just 50 pieces."

Primates

Six subgroups exist today - lemurs, lorises, tarsiers, New World monkeys, Old World monkeys, apes, humans

Dwarf lemur is closest modern match

Primitive primate ancestor was small-brained

According to the new work, the earliest common ancestor of all primates was probably a nocturnal, tree-living creature with grasping hands and feet.

It weighed just a few pounds and dined on fruit and insects.

The females gave birth to a single offspring, which clung to their fur.

Co-author Dr Christophe Soligo of the Natural History Museum in London, UK, said the new work put specific events within primate evolution into a very different context.

"The world 85 million years ago was very different to the world 65 million years ago," he told the BBC.

"What we demonstrate is that modern orders of mammals appeared well before dinosaurs disappeared so the initial divergence of modern orders of mammals cannot be the result of the extinction of the dinosaurs."